The present invention relates in general to substrate manufacturing technologies and in particular to an apparatus for ion incident angle control and/or for polymer control and methods therefor.
In the processing of a substrate, e.g., a semiconductor substrate or a glass panel such as one used in flat panel display manufacturing, plasma is often employed. As part of the processing of a substrate for example, the substrate is divided into a plurality of dies, or rectangular areas, each of which will become an integrated circuit. The substrate is then processed in a series of steps in which materials are selectively removed (etching) and deposited. Control of the transistor gate critical dimension (CD) on the order of a few nanometers is a top priority, as each nanometer deviation from the target gate length may translate directly into the operational speed of these devices.
Areas of the hardened emulsion are then selectively removed, causing components of the underlying layer to become exposed. The substrate is then placed in a plasma processing chamber on a substrate support structure comprising a mono-polar or bi-polar electrode, called a chuck or pedestal. Appropriate etchant gases are then flowed into the chamber and struck to form a plasma to etch exposed areas of the substrate.
A common etching method is RIE or reactive ion etch. RIE combines both chemical and ion processes in order to remove material from the substrate (e.g., photoresist, BARC, TiN, Oxide, etc.). However, the pressure to further reduce substrate feature sizes, as well as the implementation of newer optimized substrate materials, has challenged current fabrication technologies. For example, it is becoming increasing difficult to maintain the uniformity or process results from the center to the edge of larger substrates (e.g., >300 mm). In general, for a given feature size, the larger the size of the substrate, the greater the number of devices on the substrate near the edge. Likewise, for a given substrate size, the smaller the feature size, the greater the number of devices on the substrate near the edge. For example, often over 20% the total number of devices on a substrate is located near the perimeter the substrate.
Due to substrate edge effects, such as electric field, plasma temperature, and the loading effects from process chemistry, the process results near the substrate edge may differ from the remaining (center) area of the substrate. For example, the equipotential lines of the plasma sheath may become disrupted, causing non-uniform ion angular distribution around the substrate edge.
Referring now to FIG. 1, a simplified diagram of a capacitively coupled plasma processing system is shown. In general, a source RF generated by source RF generator 110 is commonly used to generate the plasma as well as control the plasma density via capacitively coupling. In other configurations, multiple RF generators may be used.
Generally, an appropriate set of gases is flowed through an inlet in upper electrode 102, and subsequently ionized to form a plasma 104, in order to process (e.g., etch or deposit) exposed areas of substrate 106, such as a semiconductor substrate or a glass pane, positioned with an edge ring 112 (e.g., Si, etc.) on an electrostatic chuck 108, which also serves as a powered electrode. Certain etch applications may require the upper electrode to be grounded with respect to a lower electrode frequency RF signal within ˜20 KHz thru 800 KHz. Other etch applications may require the upper electrode to be grounded with respect to a lower electrode RF signal that is at least one of 2 MHz, 27 MHz, and 60 MHz. Still other etch application may require the upper electrode to be grounded with respect to all of the RF signal frequencies previously mentioned.
Edge ring 112 generally performs many functions, including positioning substrate 106 on chuck 108 and shielding the underlying components not protected by the substrate itself from being damaged by the ions of the plasma edge ring 112 may further sit on coupling ring 120 (e.g., quartz, etc.), which is generally configured to provide a current path from chuck 108 to an edge ring 112.
In general, it is desirable for the electric field to remain substantially constant over the entire surface of the substrate in order to maintain process uniformity and vertical etch profiles. However, because of plasma chamber conditions and/or configuration, a potential difference may exist between chuck 108 and the edge ring 112. Consequently, this potential difference may create a non-uniformity 122 in the plasma sheath shape, and hence adversely affect the etch profile.
In addition, during the etch process, it is not uncommon for polymer byproducts (e.g., fluorinated polymers, etc.) to form on the substrate backside and/or around the substrate edge. Fluorinated polymers generally comprise photoresist material previously exposed to an etch chemistry, or polymer byproducts deposited during a fluorocarbon etch process. In general, a fluorinated polymer is a substance with a chemical equation of CxHyFz, where x, z are integers greater than 0, and y is an integer greater than or equal to 0 (e.g., CF4, C2F6, CH2F2, C4F8, C5F8, etc.).
However, as successive polymer layers are deposited on the edge area as the result of several different etch processes, organic bonds that are normally strong and adhesive will eventually weaken and peel or flake off, often onto another substrate during transport. For example, substrates are commonly moved in sets between plasma processing systems via substantially clean containers, often called cassettes. As a higher positioned substrate is repositioned in the container, a portion of a polymer layer may fall on a lower substrate where dies are present, potentially affecting device yield.
Referring now to FIG. 2, a simplified diagram of a substrate in which a set of edge polymers have been deposited on the planar backside is shown. As previously stated, during the etch process, it is not uncommon for polymer byproducts (edge polymers) to form on the substrate. In this example, the polymer byproducts have been deposited on the planar backside, that is, the side of the substrate away from the plasma. For example, the polymer thickness may be about 250 nm at about 70° 202, 270 nm at about 45° 204, and about 120 nm at 0° 206. In general, the greater the thickness of the polymer, the higher the likeliness that a portion of the polymer may become dislodged and fall onto another substrate or the chuck, potentially affecting manufacturing yield.